In ophthalmology, optimal visualisation and ease of surgical manipulation are the cornerstone for successful surgical results. Despite considerable technical progress, some ocular structures remain inaccessible due to interposed opaque dioptric media or due to their location. The endoscope's ability to bypass anterior segment opacities and reach the innermost regions of the eye gives it a unique advantage in surgeries involving structures in the ciliary body region and in vitreoretinal surgeries in eyes with opaque or damaged anterior segments.
Types of microendoscopes
Microendoscopes can be fibre-optic or non-fibre-optic:
- In the fibre-optic version, optical fibres for illumination, imaging and laser photocoagulation extend from the console interfaces through a handpiece to the distal end of an intraocular probe. The high-resolution optical image from the intraocular tip is transmitted via the optical fibres to its proximal end, which is interfaced with a digital video camera.
- In a microendoscope based on non-fibre-optic or Gradient Index (GRIN) lenses, the lenses are replaced with small-diameter GRIN lenses that are manufactured with flat ends to facilitate their use in multi-lens systems and possible attachment to fibre-optic components. In this system, the camera or viewing eyepiece is directly connected to the GRIN intraocular probe-lens handpiece, so the system is more fragile.
The coaxial optical property of the ocular endoscope gives a better view of the vitreous than conventional imaging systems. The intraocular depth of field varies from approximately 0.75 to 40 mm, allowing high magnification when the endoscope probe is adjacent to tissue and a panoramic intraocular view when close to the sclerotomy site.
Applications of endoscopy
The ability to bypass anterior segment opacities makes the endoscope a very useful tool for early intervention in vitreoretinal procedures, eliminating the need to combine it with keratoplasty or keratoprosthesis and allowing for a better surgical and functional outcome. Due to the improved visualisation of the anterior retina, vitreous base, pars plana and ciliary groove, without structural distortion, the usefulness of endoscopy is particularly evident in advanced diseases such as endophthalmitis, anterior proliferative vitreoretinopathy (PVR), tractional retinal detachment (TRD) and in eyes with damaged anterior segment, where direct visualisation of the retina and optic nerve helps decide whether to perform or avoid complex surgical procedures in eyes with uncertain visual potential.
Ocular endoscopy facilitates the diagnosis and treatment of anterior segment pathologies related to the ciliary body, anterior chamber angle, posterior iris epithelium and capsular support, and is useful for intraocular lens (IOL) placement. These are all areas that are difficult to access and visualise with a conventional microscope.
Furthermore, endoscopic cyclophotocoagulation via the anterior approach or via pars plana has proven to be a successful treatment modality for patients with glaucoma, including congenital or paediatric glaucoma, obviating the need for early surgery.
Technological advances in ocular endoscopy
One of the most important disadvantages of ocular endoscopy is the two-dimensional (2D) images that can be obtained. Therefore, recent innovations include the development of a 3D endoscopy system.
Ophthalmic microendoscopes traditionally have rigid intraocular probes, straight or curved depending on use, for posterior or anterior surgery. Disposable illumination and laser probes with extendable curved fibre-optic bundles housed within a rigid intraocular probe are also available. Potentially, the illumination and imaging channels can be colour filtered to perform monochromatic endoscopic ophthalmoscopy or even fluorescein angiography. Although still in the developmental stage, it is likely that intraoperative OCT (optical coherent radiation tomography) data could be made available during microendoscopic procedures from sources such as microscope-integrated OCT systems, stand-alone intraocular OCT probes or very small-diameter OCT probes integrated into microendoscopes.
In conclusion, intraocular endoscopy is certainly a promising and developing technique. In its current form, it is a valuable resource for the surgeon for complex procedures involving the posterior segment and the ciliary body region.
Bibliography:
Dr. Carmelo Chines
Direttore responsabile
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